1. Field of the Invention
This invention relates to an improvement of a screw or self tapping screw which is suitable for fastening a panel member as a building wall or a ceiling or the like, for example, to a ground material at a main structure side.
2. Description of the Prior Art
This type of screw or self-tapping screw in the prior art is defined in general as a dry wall screw or the like and constructed as shown in FIG. 6, for example. This screw 50 is used for fastening a panel member such as a gypsum board 62 applied under tension over a surface of a steel ground material 61 of a light weight type steel or the like constituting an edge of a structure at a main structure side such as a building wall or a ceiling as shown in FIG. 7, for example.
As this ground material, in addition to the aforesaid steel ground material 61, there are wooden structural materials such as wood or particle board and further as a panel member, there are a plywood, a hard board, a flexible board or the like in addition to the aforesaid gypsum board 62.
However, the screw of the present invention can be used for fastening various types of panel members to various types of ground materials and in particular the most preferable effect can be attained if the present invention is applied to a steel ground material having a thin wall, a hard panel and a fragile gypsum board.
The screw of the prior art type described above is comprised of a screw shaft part 53 having threads 52 at an outer circumference of a shaft part 51 of a straight column-like shape, a drilling part 54 connected to an extreme end of the screw shaft part 53 and a head part 55 arranged at a rear end part of the screw shaft part 53.
The drilling part 54 is formed with a tapered shaft part 56 formed to have a gradually decreased diameter from the shaft part 51 toward its extreme end and an extreme end thread 57 connected to the thread 52 at an outer circumference of the tapered shaft part 56, wherein the fastening is carried out while the drilling part 54 cooperates with the screw shaft part 53 to perform a punching and a threading.
The aforesaid head part 55 has a circular shape at a flat upper surface 58 of which outer circumferential edge is concentrically projected widely in a radial direction from the aforesaid shaft part 51, and the head part 55 is provided with an engaging groove 60 such as a cross-shaped hole where a screw driver tool is engaged with a central part of the upper surface 58. A seat surface 59 of the head part 55 extending from the outer circumferential edge of the upper surface 58 to the aforesaid shaft part 51 is formed with an inverse truncated cone having a curved concave surface in which its outer circumference is gradually decreased in its diameter, converged into a shaft diameter of the shaft 51 and gently sloped along an axial direction so as to hold the gypsum board 62 with a strong holding force upon completion of the fastening action, i.e., an entire shape of the head 55 is formed to a trumpet-shape.
The screw to which the present invention pertains is not limited to a tapping screw structure as described above, but it can be applied to a screw of a self-drilling structure in which a drilling part having a drill end acting as a self-punching action similar to that of the general type of a drill blade is formed at an extreme end of the aforesaid screw shaft part, the drilling part performs a punching action and the threads 52 of the screw shaft part 53 are subsequently applied for making a screw setting, for example, a self-tapping screw disclosed in the gazette of Jap. U. M. Publn. No. Hei 2-29294.
As described above, in case that the panel member is the gypsum board 62, an additive agent is added to the gypsum of the base material, since solidified into a plate form and the gypsum board is fragile, the protection sheets 64 and 65 having superior adhering characteristic and coating characteristic such as a cardboard or a fiber or the like are applied to both surfaces of the gypsum plate 63 with an adhesive agent.
When the gypsum board 62 is to be fixed, as shown in FIG. 7 (a), an extreme end of the screw driver tool 66 is engaged in the engagement groove 60 of the screw 50, the screw driver tool 66 is rotated and the drilling part 54 of the screw 50 is pierced into the gypsum board 62. With such an arrangement, the drilling part 54 reaches the steel ground material 61 while punching in sequence against the gypsum board 62, the punching and threading are carried out in the steel ground material 61, subsequently the screw shaft part 53 is threadably fitted to the steel ground material 61, and the fastening is completed while, as shown in FIG. 7(b), the upper surface 58 of the head part 55 is flush with the surface of the gypsum board 62 or preferably the upper surface is being slightly recessed. After this state, the upper surface 58 of the head part 55 containing the engaging groove 60 and the recessed surface of the gypsum board 62 generated at an outer circumferential edge are filled with a putty coating 67 so as to make a uniform surface for applying a cloth or a paint over an entire surface area of the gypsum board 62 is made so as to perform a finishing process with an ornamental material 68.
However, in case of the screw 50 having the structure of the prior art as described above, the screw has the following several problems to be improved.
In case of the aforesaid screw 50, at first, the drilling part 54 at the extreme end thereof is formed with a sharp shape in order to improve a performance of screwing action during a punching operation, a carbon sintering treatment is carried out for the screw and at the same time a seat surface 59 is formed with a trumpet shape so that the gypsum board 62 can be pressed with a strong holding force upon completion of the fastening work.
However, since the seat surface 59 has no cutting capability and an entire circumferential surface of the seat surface 59 is concurrently contacted with the gypsum 63 during the screwing action so as to act as a substantial resistance, it requires a substantial thrusting force (a pushing force). Consequently, there is a possibility that an application of excessive thrust force causes the thread formed in the steel ground material 61 to be destroyed or the screw is fastened while the upper surface 58 of the head 55 is being floated away from the surface of the gypsum board 62.
In particular, in the event that a thickness of the steel ground material 61 is thin and the gypsum board 62 has a high hardness, even if a cutting force of the drilling part 54 is improved as described above and a screwing torque for use in punching the steel ground material 61 is reduced, it becomes necessary to provide a larger thrusting force than the screwing torque for pushing the head part 55 as described above, resulting in that the thread screwed at the steel ground material 61 is damaged and the screw 50 runs idle. As a result, the screw is fastened with the upper surface 58 of the head part 55 floated up away from the surface of the gypsum board 62, a sufficient supporting force can not be attained for the gypsum board 62, and at the same time a certain trouble may occur in a finishing process with an ornamental material 68 as described below.
It is preferable that a height of the upper surface 58 of the head part 55 upon completion of the fastening operation is in such a degree to be slightly concaved from the surface of the gypsum board 62 so as to enable the concave surface to be repaired with a putty coating 67. However, the upper surface 58 of the head part 55 is projected from the surface of the gypsum board 62 due to the aforesaid reasons, or the height of the upper surface 58 of the head 55 in respect to the surface of the gypsum board 62 is not made constant due to characteristics of the steel ground material 61 and the gypsum board 62 as well as irregularity in of the fastening force. Due to this fact, the upper surface 58 of the head part 55 is projected, resulting in that the projected surface can not be required with the putty coating 67 and even in the case of the flushed surface, the metallic surface has a poor putty applicability thereon. Further, the upper surface 58 of the head part 55 may not be applied with the putty coating 67 in sufficient thickness and so the putty coating 67 may easily be peeled off when dried, and even if a finishing process with an ornamental material 68 is carried out, so irregular corrugated portions are generated and a uniform and superior finished surface can not be attained.
The protection sheet 64 broken by a screwing action of the screw 50 is brought into the gypsum 63 by a pushing action of the heat part 55, the protection sheet 64 is peeled off as it is and as shown in FIG. 8, the peeled-off partial broken piece 64a can not be pressed with the seat surface 59 but wound around the seat surface 59 in an irregular state, resulting in that upon completion of the fastening operation of the screw, a seating state of the seat surface 59 is made inferior and the seating is made unstable while the head part 55 is inclined or floated and then its supporting force against the gypsum board 62 is reduced.
In addition, the partially bulged-out and finely peeled piece 64b protruds outwardly from an outer circumferential edge of the head part 55 upon completion of fastening operation. If the finishing process with the putty coating 67 or the ornamental material 68 is carried out while the peeled piece 64b is being kept as it is, some corrugated portions are generated and a uniform and superior finished surface may not be attained, so that a quite troublesome manual operation is required for cutting the corrugated portions or grinding off with a sandpaper.
In view of the foregoing, it is an object of the present invention to provide a screw or self-tapping screw capable of improving these problems.
It is also an object of the present invention to provide a screw or self-tapping screw to which fitting of a screw driver tool can be accurately and easily carried out.
It is a still further object of the present invention to provide a screw or self-tapping screw in which resistance during a threading operation of the screw is reduced and performance of the threading operation is improved.
It is a still further object of the present invention to provide a screw or self-tapping screw in which an idle rotation of a screw caused by an excessive thrust force is prevented and a supporting force of the screw is improved.
It is an object of the present invention to provide a screw or self-tapping screw in which a head part is buried in a target surface upon completion of a fastening operation and the screw is suitable for a finishing work such as a putty coating or the like.
It is also an object of the present invention to provide a screw or self-tapping screw in which a breakage of a covering protection sheet on the target surface is prevented to improve a supporting force of the screw.
It is also an object of the present invention to provide a screw or self-tapping screw which is suitable for preventing a turning-up of a covering protection sheet on the target surface as well as its fine split and for improving a surface finishing work.
Other objects and advantages of the present invention will become apparent from the description of the preferred embodiments in reference to the accompanying drawings.